1. Field of the Invention
The present invention relates generally to rheometers, which are used to characterize materials by measuring the materials viscosity, elasticity, shear thinning, yield stress, compliance and/or other material properties.
2. Background of the Invention
Rotary rheometers, viscometers or viscosimeters are used to measure fluid or other properties of materials such as their viscosity by rotating, deflecting or oscillating a measuring object in a material, and measuring, for example, the torque required to rotate or deflect or oscillate the object within the material. As used herein, the term xe2x80x9crheometerxe2x80x9d shall mean rheometers, viscometers, viscosimeters and similar instruments that are used to measure the properties of fluid or similar (see list below) materials. The term xe2x80x9cmeasuring objectxe2x80x9d shall mean an object having any one of several geometries, including, for example, cones, discs, vanes, parallel plates, concentric cylinders and double concentric cylinders. The materials may be liquids, oils, dispersions, suspensions, emulsions, adhesives, biological fluids such as blood, polymers, gels, pastes, slurries, melts, resins, powders or mixtures thereof. Such materials shall all be referred to generically as xe2x80x9cfluidsxe2x80x9d herein. More specific examples of materials include asphalt, chocolate, drilling mud, lubricants, oils, greases, photoresists, liquid cements, elastomers, thermoplastics, thermosets and coatings. As is known to one of ordinary skill in the art, many different geometries may be used for the measuring object in addition to the cylinders, cones, vanes and plates listed above. The measuring objects may be made of, for example, stainless steel, anodized aluminum or titanium. U.S. Pat. Nos. 5,777,212 to Sekiguchi et al., 4,878,377 to Abel and 4,630,468 to Sweet describe various configurations, constructions and applications of rheometers.
The fluid properties of materials are generally dependent on their temperature. For that reason, it is generally important that the temperature of the material being tested is known and is homogeneous. If the temperature of the material being tested were not homogeneous, the accuracy and validity of the measurement would be seriously compromised. Thus the temperature of the fluid is generally accurately controlled, and is preferably made as homogeneous as possible, for example by using a fluid bath or a Peltier plate. Compared to a fluid bath, a Peltier plate temperature control system provides a more rapid heating and cooling of the sample, and is more economical, because it does not require an expensive controlled-temperature fluid circulator.
FIG. 1A is a schematic perspective view of a rotary rheometer 100, showing lead screw 101, draw rod 102, optical encoder 103, air bearing 104, drive shaft 105, drag cup motor 106, measuring object 107 (shown in FIG. 1A as a parallel plate), heating/cooling assembly (eg., a Peltier plate) 108, temperature sensor 110 (eg., a Pt temperature sensor), surface 111, normal force transducer 112, and auto gap set motor and encoder 113. FIG. 1B is a schematic drawing of a concentric cylinder configuration in position on the rheometer of FIG. 1A, showing the control jacket 120 of the concentric cylinder configuration on top of normal force transducer 112 of rheometer 100. FIG. 1B shows a cylindrical measuring object 121 (used in this configuration instead of the parallel plate measuring object 107 shown in FIG. 1A).
In operation, control jacket 120 contains sample cup 201. FIGS. 2A and 2B are schematic drawings of a top view and a cross-sectional view of a prior art sample cup. FIG. 2A shows sample cup 201, which has top flange 203 with top flange lip 202, and fixing holes 205. Sample cup 201 also includes sample bore 207 and cover location lip 209. Cover location lip 209 is used to locate a cover that may be used, if necessary, to minimize evaporation from the sample. FIG. 2A also shows the upper end 204 of the sample cup 201 and lower end 206 of sample cup 201. FIG. 2B shows the upper end 204 and the lower end 206 of sample cup 201, as well as fixing holes 205, sample bore 207, sample cup base 208 and location lip 209. The fixing holes are used to prevent rotation of the sample cup during a test run. As shown in FIGS. 2A and 2B, the upper end 204 of the sample cup has a larger outer diameter than its lower end 206.
FIGS. 3A and 3B are a top view and a cross-sectional view of a prior art control jacket 301. Control jacket 301 has fixing holes 303, 304, 312, and 314, top lip 302, cabling hole 305 and sensor hole 306. Fixing holes 314are used in conjunction with holes 205 (shown in FIGS. 2A and 2B) to prevent rotation of the measuring cup. Fixing holes 312 are used to fix the heating/cooling assembly, fixing holes 304 are used to fix the lower mounting plate and fixing holes 303 are used to fix the outer sleeve/cover. Sensor holes 306 and 313 are used for temperature sensors. FIGS. 3A and 3B also show cover locations 307 and 308, sample cup location chamfer 311, the outer surfaces 309 and 310 of the control jacket and the main bore of the control jacket 315 (which is where sample cup 201 fits into control jacket 301) and air hole 321. Cover locations 307 and 308 are used to locate the cover/sleeve that fits over the outer jacket. FIG. 3B also shows the heating/cooling assembly 322, which is used to heat or cool the control jacket and the sample cup. For example, heating/cooling assembly 322 may be a Peltier plate.
As shown in FIG. 3C, in operation sample cup 201 fits inside control jacket 301, such that an isolation gap is formed between sample cup 201 and control jacket 301.
U.S. Pat. No. 6,240,770 to Raffer discloses a rotary viscosimeter having an isolation gap between a measuring cup and a temperature control cup. Because of the isolation gap, the measuring cup and the temperature control cup are in good heat conducting contact only in the vicinity of their upper circumferences, such that the heat conduction between the measuring cup and the temperature control cup is restricted to the upper ends of the measuring and control cups only. A heat pump, such as a Peltier block, is used to control the temperature of the temperature control cup so that heat is supplied to the measuring cup in a controlled manner via the mutual contact area at the upper ends of the measuring and control cups.
The present invention is a rotary rheometer having a concentric cylinder configuration. The concentric cylinder configuration includes a control jacket and a sample cup. The sample cup fits snugly inside the control jacket, such that the sample cup is in substantial thermal contact with the control jacket along at least twothirds of the length of the sample cup, and preferably along the greater part of the length of the sample cup (e.g., more than 80% of the length). The sample cup and the control jacket are fabricated from a good heat conducting material, such as, for example, HE30 aluminum. Copper or silver alloys or stainless steel could also be used. A heating/cooling assembly, positioned, for example, beneath the control jacket, is used to heat and/or cool the control jacket, thus heating and cooling the sample cup. In a preferred embodiment of the invention, the heating/cooling assembly is a Peltier plate. The sample cup includes a generally annular chamber, which ensures that the sample experiences a uniform temperature.
Preferably, the bottom of the sample cup is not in contact with the bottom of the control jacket, i.e., there is a gap between the bottom of the sample cup and the bottom of the control jacket such that there is a disk-shaped lower chamber that is in fluid communication with the annular chamber in the sample cup.